1. Field of the Invention
The present invention relates generally to the construction and use of vascular catheters and, more particularly, to vascular catheters having a reduced-size distal tip capable of selectively receiving either a movable guidewire or a work element.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed limbs of the body and coronary blood vessels that feed the heart. When deposits accumulate in localized regions of the blood vessels, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, where a balloon-tipped catheter is used to dilitate a stenosed region within the blood vessel; atherectomy, where a blade or other cutting element is used to sever and remove the stenotic material; and laser angioplasty, where laser energy is used to ablate at least a portion of the stenotic material; and the like.
In order to more effectively apply such interventional techniques, a variety of vascular imaging devices and methods employed. Of particular interest to the present invention, intraluminal imaging catheters having ultrasonic transducers at their distal ends have been employed to produce images of the stenotic region from within the blood vessel.
A number of particular designs for such ultrasonic imaging catheters have been proposed. One approach has been to use a phased-array of discrete ultrasonic imaging transducers at the tip of a vascular catheter. While such an approach is advantageous in that it does not acquire mechanical manipulation of the transducers, it is problematic in that the image quality is limited. Such phased-array intravascular imaging catheters are commercially available from EndoSonics Corporation, Rancho Cordova, Calif., as the CathScanner I System.
A more promising approach for intravascular ultrasonic imaging employs mechanical rotation of the ultrasonic signal, either by mechanically rotating the transducer itself or by mechanically rotating a mirror which radially deflects the ultrasonic signal from the transducer. Such mechanical rotation generally provides a better image quality than use of a phased-array system, but the design of the catheters is problematic since the designs must provide for rotating the transducer and/or an associated mirror at speeds usually in the range from 500 to 2000 rpm. Moreover, the interior blood vessel must be protected from the rotating components which could cause substantial injury should they come in contact with the blood vessel.
A number of specific designs for mechanical ultrasonic imaging catheters have been described. An early design is illustrated in U.S. Pat. No. 4,794,931, where the mechanical components of the imaging system are located within a housing at the distal end of the catheter. The housing includes a fixed guidewire at its distal tip which is used to position the catheter within the vascular system. While the use of such fixed-guidewire designs can provide an excellent image quality, under some circumstances it is desirable to use an "over-the-wire" design where the catheter may be introduced over a separate (movable) guidewire. The use of a movable guidewire has certain advantages including improvement in steering capability through branch coronary arteries and elsewhere and facilitating catheter exchange, e.g. substitution of an interventional catheter after the imaging has been completed.
A particular design for an over-the-wire ultrasonic imaging catheter is illustrated in FIG. 1. The catheter includes the catheter body 10 having an exterior catheter lumen 12 attached near its distal end. A rotatable ultrasonic imaging assembly 14 is mounted at the distal end of the drive member 16, and the device may be introduced over a conventional movable guidewire 18, as illustrated. Such designs employing parallel lumens, however, are disadvantageous since the width of the distal tip in the region of the ultrasonic imaging element must be sufficient to also accommodate the guidewire. Ideally, to be able to cross very narrow lesions, the diameter of the catheter in the region of the imaging element should be minimized, preferably including only the imaging element to be rotated and a catheter sheath surrounding the imaging element. The requirement of the separate guidewire lumen increases this minimum size, making the design unsuitable for small blood vessel type lesions and for passing through conventional guiding catheters.
Designs of the type illustrated in FIG. 1 are commercially available from Medi-Tech, Inc., Watertown, Mass. A design similar to that of FIG. 1 is illustrated in U.S. Pat. No. 5,024,234, the disclosure of which is incorporated herein by reference.
An alternative design for a mechanical ultrasonic imaging catheter avoids the requirement for a parallel guidewire lumen by providing for exchange of the mechanical imaging components with a conventional guidewire. As illustrated in FIG. 2, such a catheter comprises a single lumen catheter sheath 20 which can receive a drive wire 22 carrying an ultrasonic imaging assembly 24 at its distal end. The catheter sheath 20 may be initially introduced over a conventional guidewire. The guidewire may then be completely removed and replaced with the imaging assembly. While the diameter of the catheter 20 may be minimized, the need to exchange the guidewire and imaging components whenever the catheter is to be repositioned is time consuming and disadvantageous. Such catheters are commercially available from Inter-Therapy, Inc., Costa Mesa, Calif. (now Cardiovascular Imaging Systems, Inc., Sunnyvale, Calif., assignee of the present application).
For these reasons, it would be desirable to provide ultrasonic imaging catheters which combine a narrow profile in the region of the ultrasonic imaging components and an ability to be introduced over a separate, moveable guidewire. It would be particularly desirable if such designs would allow for imaging within the narrow distal region of the catheter without the need to remove the guidewire from the catheter body. In particular, such imaging catheter should present a width of less than about 5 French, and more preferably being less than about 3 French, to facilitate entry into the coronary arteries and even very tight lesions.
SUMMARY OF THE INVENTION
According to the present invention, vascular catheters comprise a catheter body having a proximal end and a distal end. The catheter body includes at least a distal region extending proximally from its distal tip and a proximal region extending proximally from the proximal end of the distal region. The distal region has a reduced cross-sectional area compared to the proximal region, with the distal region typically including only a single lumen and the proximal region including at least a pair of parallel lumens.
The lumen in the distal region of the catheter body is contiguous with both of the parallel lumens in the proximal region. Thus, a drive shaft which is reciprocatably disposed in one of the lumens in the proximal region is able to be selectively advanced to the distal region or retracted back into the proximal region. The catheter body can be inserted over a guidewire by passing the guidewire through the lumen in the distal region into the other lumen at the proximal region, i.e., the lumen which is not occupied by the drive shaft. A work element, typically an ultrasonic imaging transducer, is mounted at the distal end of the drive shaft and can be moved in and out of the distal region by reciprocating the drive shaft.
In use, the catheter body can be introduced over a movable guidewire (or equivalent structure) which has been previously positioned at a desired location within the vascular system. The catheter body is manipulated until the distal region lies within the location of interest, typically a stenotic lesion. Once the catheter body is in position, the movable guidewire can be retracted (i.e. pulled in the proximal direction) so that it evacuates the lumen in the distal region but remains within a lumen in the proximal region. The work element on the drive shaft, typically an ultrasonic transducer, can then be advanced in the distal direction so that it enters the lumen in the distal region. Imaging or another interventional technique may then be performed using the work element, and, after completion, the work element may be retracted into its lumen within the proximal region. The guidewire can then be advanced through the distal region and the catheter body repositioned over the guidewire so that the distal region is moved to another location of interest.
In another aspect, the present invention can provide an improved catheter body which can act as a guiding sheath for positioning and repositioning a variety of working catheters, including ultrasonic imaging catheters, interventional catheters, and the like. Such guiding catheters comprise a catheter body including a tubular member having a proximal end and a distal end, wherein the tubular member includes a proximal region having at least two lumens and a distal region having a single lumen which is connected to and in communication with said at least two proximal lumens. The distal lumen will have a cross-sectional area which is less than the combined cross-sectional areas of the two lumens of the proximal region. In this way, the guiding catheter can provide a low profile at its distal end, while maintaining a guidewire and at least one working catheter within the proximal lumens. In a particular embodiment, a second working catheter can be introduced over the movable guidewire in the proximal lumen and selectively through the single distal lumen into the blood vessel.
In an exemplary embodiment, the guiding catheter of the present invention includes three proximal lumens, with a guiding catheter in a first of the proximal lumens, an ultrasonic imaging catheter core in a second of the proximal lumens, and an interventional catheter, e.g., a balloon angioplasty catheter, in a third of the proximal lumens. Such guiding catheters can be initially positioned and subsequently repositioned with the guidewire positioned through the single distal lumen. While the guidewire is in the single lumen, both the imaging catheter and the interventional catheter will be retracted within the proximal lumens. After the distal end of the guiding catheter is positioned within a desired region, typically a stenosed region, the guidewire will be retracted and replaced with either the imaging or interventional catheters, usually the imaging catheter in order to provide an initial evaluation of the stenosed region. After imaging the stenosed region, the imaging catheter can be retracted and replaced by the interventional catheter, e.g., a balloon angioplasty catheter. Usually, the guiding catheter will be retracted sufficiently to expose the balloon on the balloon catheter to the stenosed region. The stenosed region can then be treated in a conventional manner, and the balloon angioplasty catheter subsequently retracted back into the proximal lumen of the guiding catheter. The distal end of the guiding catheter can then be repositioned within the region of stenosis, the imaging catheter core returned to the proximal end, and the stenosed region reevaluated by ultrasonic imaging. The region can then be retreated, if necessary, or the guiding catheter can be repositioned to another location using the guidewire in a conventional manner. Optionally, in the three lumen embodiment, a third working catheter (in addition to the imaging assembly and second working catheter just described) could be introduced over the movable guidewire in the proximal lumen and through the single distal lumen into the blood vessel.
Thus, the present invention provides an intravascular catheter which combines a distal region having a minimum cross-sectional area to facilitate entry into coronary arteries and very tight stenotic lesions with the ability to introduce the catheter over a movable guidewire and retain the guidewire in place during imaging or another interventional procedure.